ISOLAPOTAMIDAE Bott, 1970

Brandis, Dirk, 2002, On the taxonomic status and biogeography of the Isolapotamidae Bott, 1970 (Decapoda, Brachyura), Journal of Natural History 36 (11), pp. 1291-1339 : 1298-1300

ISOLAPOTAMIDAE Bott, 1970

(gures 2b, 4)

Isolapotamidae Bott, 1970a: 333 ; Bott, 1970b: 190; Dai et al., 1979: 122.

Potamidae Ng and Yang, 1986: 15 ; Ng, 1986b: 216; Ng and Tan, 1998: 53.

Potamidae (part.): Dai, 1999: 85.

Type genus. Isolapotamon Bott, 1968 (by original designation).

Diagnosis. Second gonopod elongated, terminal tube very narrow in cross-section, strongly sclerotized and stiOE; fused zone formed by a hook-like edge to which other edge perfectly adjusts; tubular cuticle with net-like structure, narrow, fused in nearly all parts with outer cuticle.

Distribution. Borneo, Malaysia, West to Central Thailand, Eastern and Southern Burma, Hainan, South and South-East China, Taiwan, Philippines, Ryukyu Islands.

Remarks. The family was established by Bott (1970a) for species of the genus Isolapotamon from Borneo and the Philippines. Bott characterized the family exclusively by the terminal joint of the rst gonopod, which is longer than the subterminal joint or short and stout, distally often broader than basically. Bott included three genera Isolapotamon , Nanhaipotamon and Malayopotamon in this family. Later, the Isolapotamidae were synonymized with the Potamidae ( Ng, 1986b, 1988a; Ng and Takeda, 1986; Ng and Yang, 1986; Ng and Tan, 1998) as distinct characters separating this family from the other Asian freshwater crabs were apparently lacking. This is de nitely correct if carapace and rst gonopod characters are taken into account.

The present study shows clearly that the morphology of the second gonopod of Isolapotamon is very characteristic, and is similar to that of other genera from Thailand, Malaysia, South China and adjacent regions (gure 4). The morphology of the terminal tube of the second gonopod is constant within this group and distinctly diOEerent from that of the second gonopod of Potamon , the type genus of the Potamidae and from that of Sinopotamon , the type genus of the Sinopotamidae , as described above (gure 2). Morphologically, there is no transition between these morphotypes and every type is characteristic for a special geographic region. In contrast to this distinct characterization of groups, the status of the Potamidae , as currently de ned, is very unclear. The Potamidae are presently characterized according to the classi cation concept of Bott (1970a, 1970b). Bott characterized the Potamidae within the Potamoidea exclusively by the three-segmented mandibular palp. The presently used concept for the classi cation of the Potamidae basing on Bott’s concept is not useful due to several problems:

The four-segmented gonopod was a morphological misunderstanding, as has been described above and thus has to be reconsidered as three-segmented.

Concerning the carapace, there are many potamid species, which show a very similar shaping and sculpturation, but in several regions occur species

Taxonomy and biogeography of the family Isolapotamidae 1299 which diOEer clearly from the others (e.g. Thaiphusa Ng and Naiyanetr, 1993 ; Thaipotamon Ng and Naiyanetr, 1993 ; Lobothelphusa Bouvier, 1917 ; Acanthopotamon Kemp, 1918 ). This means, within the Asian potamoid crabs, there are no carapace features which can be used consistently for the characterization of the entire family Potamidae .

As stated by Cumberlidge (1999), the two-segmented mandibular palp is a distinct feature to characterize the Potamonautidae . As far as presently known, in all Asian potamoid freshwater crabs the mandibular palp is three-segmented. However, this is not an exclusive character of the Asian freshwater crabs, the same type of mandibular palp can also be observed in many marine crabs as in Carpiliidae Ortmann, 1893 ; Cancridae Latreille, 1803 or Mennippidae Ortmann, 1893 and might thus be a plesiomorphic state not useful as a de nition character of the Potamids.

This means that the morphology of the copulatory apparatus, especially that of the second gonopod, remains the only consistent character set. Every morphotype of the second gonopod is characteristic for a number of Asian crab genera and is related to a special geographic region. Each of these types is characteristic for one of the type genera of the formerly described South-East Asian potamoid families. Thus, it is possible to distinguish the three families Potamidae , Sinopotamidae and Isolapotamidae on the basis of the second gonopod morphology thus diOEering from Bott’s circumscriptions. As concerns taxonomic ranking, in any case the Isolapotamidae and Sinopotamidae have to be treated at the same taxonomic level. This is the family rank in the presently accepted system. It might be that the status of these groups has to be changed to subfamily level. This can, however, only be done after the taxonomic and phylogenetic relations between Potamoidea , Gecarcinucoidea and the American freshwater crabs are analysed in detail. Until then a change in ranking does not solve any problems, but creates new confusion.

In summary, the family Isolapotamidae can only be characterized consequently by a second gonopod with a very narrow tube and a characteristic contact zone. It is also obvious that this morphotype represents a special sperm transfer strategy. Morphological features supporting this theory are:

the very stiOE cuticle of the terminal tube of the second gonopod;

the fusion of the tube margin with the outer cuticle, rendering the walls of the tube massive and thus indicating a strong stabilization;

the narrow tube lumen;

the characteristic contact zone of the lateral margins closing the tube very tightly lengthwise.

Malayopotamon is here excluded from the Isolapotamidae , because its second gonopod is morphologicall y very diOEerent from that of Isolapotamon as well as from those of Potamon and Sinopotamon .

In spite of the morphological constancy of the second gonopod, the rst gonopod within the family Isolapotamidae is very variable especially in the shape of the terminal joint and the exible zone. Its morphology and shape is, therefore, not useful for taxonomic classi cation of higher ranks.